1. Field of the Invention
The invention is directed to a radiation-emitting semiconductor component having a semiconductor body that comprises a radiation-generating active layer, having a central front-side contact on a front side of the semiconductor body and a back-side contact on a back side of the semiconductor body for impressing a current into the semiconductor body containing the active layer.
2. Description of the Related Art
In light-emitting diodes, the current for operating the light-emitting diode is usually sent from a central contact on the upper side through the semiconductor to a surface-wide back-side contact. A fundamental problem is how to distribute the current density in the light-generating layer as uniformly as possible onto the entire chip area.
For solving this problem, one or more current-expanding layers are applied on the chip surface between the active zone and the central contact. The current-expanding is set using a suitable selection of the layer thickness and of the electrical properties of the expanding layers.
The current-expanding layers are usually composed of p-doped GAP in the case of light-emitting diodes that are based on the InGaAlP material system
In the manufacture of thin-film LEDs, the window layer is usually grown onto the substrate before the active layer and becomes the upper side of the LED only after the transfer onto a new carrier and the stripping of the substrate. Due to the great difference in the lattice constants of about 4%, however, it is currently not possible to deposit active layers of sufficient quality on GAP. This makes the manufacture of InGaAlP thin-film LEDs with current-expanding layers difficult.
Other proposed solutions are to provide structured contact patterns or transparent contacts such as thin metal layers or contacts of indium tin oxide (ITO). Each of these solutions, however, has disadvantages. A metal layer exhibits a light absorption that cannot be neglected, whereas a contact layer of ITO generally forms a relatively poor electrical contact to the semiconductor.
Up to now, for example, very thin, semi-transparent contact layers were employed for the terminal contacts, as disclosed, for instance, by U.S. Pat. No. 5,767,581 on a semiconductor chip on the basis of InAlGaN. In order to assure a high transparency of the terminal contacts, the semi-transparent layers must be fashioned optimally thin. This is opposed by the demand for adequate homogeneity, adequate shunt conductivity and low contact resistance. The semitransparent contact layers employed for traditional light-emitting diodes therefore necessarily absorb a large part of the light emerging through the surface.
Over and above this, the known optoelectronic components on the basis of InAlGaN with semi-transparent contacts can fail given a high thermal/electrical load due to a degradation of the contact layer.
Furthermore, German Patent Document DE 1 99 27 945 A1 discloses that a contact layer having a thickness of 1000 through 30000 xc3x85 be applied onto the p-doped layer of a light-emitting diode on the basis of InAlGaN. Openings having a width of 0.5 through 2 xcexcm are introduced in this contact layer in order to enable an improved light transmission through the contact layer.
The present invention is based on the object of providing a radiation-emitting semiconductor component of the species initially cited that avoids the disadvantages of the prior art. In particular, an adequately large-area impression of current into the light-generating layer should be achieved for systems in which the application of high-quality active layers on current-expanding layers takes on a difficult and complicated form.
This object is achieved by a radiation-emitting semiconductor component having a semiconductor body, the semiconductor body comprising a radiation-generating active layer, a central front-side contact on a front side of the semiconductor body, a back-side contact on a back side of the semiconductor body for impressing a current into the semiconductor body containing the active layer, the back-side contact comprises a plurality of contact locations spaced from one another, a size of the contact locations increasing with increasing distance from the central front-side contact.
Advantageous developments include having the size of the contact locations and a spacing of the contact locations from one another are selected such that a flow of current through the active layer is essentially homogeneous during operation. The contact locations may be formed by circular or rectangular contact points of different diameter or width. A majority of spaced contact locations may contain several groups of contact locations of a respectively same size, these contact locations of each group being arranged with essentially the same spacing from the central front-side contact and concentrically around a common mid-point on a back side of the semiconductor body. An insulation layer may be used to separate the spaced contact locations. Trenches may be introduced in the semiconductor body that separate the spaced contact locations. The component may comprise a plurality of spaced conical or pyramidal frustums introduced into a back side of the semiconductor body, respective contact locations being arranged on their cover surfaces. A size of the conical or pyramidal frustums may be constant and an area of the contact locations arranged on the cover surfaces may increase with increasing distance from the central front-side contact. Finally, the component may be configured such that the contact locations can be electrically contacted via a carrier for eutectic bonding that is provided with bond metal. More details of the embodiments are described below.
Inventively, the back-side contact in a radiation-emitting semiconductor component of the species is designed such that is comprises a plurality of contact locations spaced from one another in which the size of the contact locations increases with increasing distance from the central front-side contact.
The invention is thus based on the idea of replacing the traditional, surface-wide back-side contact with a non-uniform distribution of contact locations. The intermediate resistance is varied with the size of the contact locations.
Since the size of the contact locations inventively increases with increasing distance from the central front-side contact, the resistance is higher in the center of the semiconductor body and drops toward the edge of the semiconductor body. A desired current profile can thus be set by the selection of size and spacing of the contact locations.
Preferably, the size of the contact locations and the spacing of the contact locations from one another are selected such that the flow of current through the active layer is essentially homogeneous during operation.
The contact locations are preferably formed by contact points having an arbitrary shape. Especially advantageous developments include having the contact locations formed by circular or rectangular contact points of different diameters or widths.
It is especially advantageous when the majority of spaced contact locations contains several groups of contact locations of the respectively same size and where the contact locations of each group are arranged with essentially the same spacing from the central front-side contact and concentrically around a common mid-point on the back side of the semiconductor body.
According to a preferred embodiment, the spaced contact locations are separated from one another by an insulation layer.
Alternatively or additionally, the spaced contact locations can also be separated from one another by trenches introduced in the semiconductor body. To that end, a plurality of spaced conical or pyramidal frustums can be introduced into the back side of the semiconductor body with respective contact locations being arranged on their cover surfaces.
In particular, the size of the conical or pyramidal frustums may be constant and the area of the contact locations arranged on the cover surfaces may increase with increasing distance from the central front-side contact.
The contact locations are preferably electrically contacted via a carrier for eutectic bonding that is provided with bond metal.